1. Field of the Invention
The present invention relates to novel .beta.-lactam antibiotics and pharmaceutically acceptable salts and esters thereof. More particularly, the present invention relates to novel cephem compounds having antibacterial activity and pharmaceutically acceptable salts and esters thereof.
2. Background Art
Cephem antibiotics exhibit excellent antibacterial activity with low toxicity for mammals. They are therefore very important to the treatment of infectious diseases in mammals. In recent years, cephem derivatives having an aminothiazolylacetyl group at the 7-position of the cephem ring have been found to have potent antibacterial activity and stability against .beta.-lactamase, leading to numerous studies and developments in these cephem derivatives. Various semi-synthetic cephem compounds have already been put on the market and clinically used as therapeutic agents for various infectious diseases.
However, among these compounds, those usable as a therapeutic agent having antibacterial activity against Pseudomonas aeruginosa and Myxomycetes are limited. Further, these compounds are unstable against .beta.-lactamase produced by resistant bacteria and have drawbacks such as low antibacterial activity against the resistant bacteria which have posed a clinical problem these days. Furthermore, many cephem antibiotics have been developed for use in injections, and it is often pointed out that, in the case of oral administration, the cephem antibiotics have low absorption ratio and, hence, have unsatisfactory efficacy.
Specific examples of .beta.-lactam compounds known in the art include Cefixime, Cefdinir, ME 1207 (Cefditren pivoxil), and ME 1206 (Cefditren).
However, no compounds having a .beta.-substituted vinyl side chain, especially a .beta.-(substituted or unsubstituted imidazo5,1-b!thiazolyl)vinyl group, at the 3-position of the cephem ring have been reported so far as the present inventors know.